Can someone explain to me the current rationale in the US left around abortion being a hot topic and a strong vote puller? As far as I can see, their arguments

Can someone explain to me the current rationale in the US left around abortion being a hot topic and a strong vote puller? As far as I can see, their arguments have devolved to weasel wording alone, like saying it's a "reproductive health" or "reproductive rights" issue. They seem to be carefully avoiding the central issue that, if discussed, could undermine all that weasel wording. I.e. the question of at what point life begins. Also correct me if I'm wrong, but in the US left, and in some states governed by them, it's the case that a unborn baby of an age which would have been a viable albeit premature birth can be killed under the wording of "aborting a pregnancy"? I'd just really like to understand the mental and philosophical basis behind this.